Such method may for instance be used in Session Initiation Protocol (SIP) signaling to/from a SIP User Agent (UA). A SIP UA may send SIP requests to an Internet Protocol (IP) Multimedia Subsystem (IMS) network and may receive SIP responses from the IMS network. These SIP requests and responses may be exchanged during SIP session establishment, during an established SIP session and for non-session related SIP message exchange.
A SIP message, i.e. a SIP request or a SIP response, may contain various headers. These headers may be used for SIP message routing or for application handling. Certain SIP headers may contain a host name or a domain name. The UA may, when receiving such host name or domain name in the SIP message, have to use this host name or domain name for processing the message.
Examples of a host name in a SIP message are:
Alert-Info: <http://www.provider.com/sounds/ringtone1245.wav>
The Alert-Info header may be used as pointer to a ring tone in a SIP Invite request or as a pointer to a ring-back tone in a SIP180 Ringing response on the Invite request.
  Call-Info:<http://www.provider.com/johnny/picture.jpg>;purpose=icon,
The Call-info provides additional information about the calling party to the called party (in the case that the Call-info header is included in a SIP request) or provides additional information about the called party to the calling party (in the case that the Call-info header is included in a SIP response).
When a SIP UA receives a message including a host name and wants to process the message, the UA may have to apply Domain Name Server (DNS) name resolving on the host name. For example, when a SIP UA receives a SIP Invite including the Alert-info header as depicted in the above example, then the UA has to contact DNS in order to resolve www.provider.com into an Internet Protocol (IP) address, so it can access that host, using HyperText Transfer Protocol (HTTP), for obtaining the ring tone from that host (/sounds/ringtone1245.wav).
DNS name resolving by the user agent (UA) may lead to delay in accessing the host associated with the host name or domain name in the message. The UA would have to send a DNS query message, or several DNS query messages, to its DNS (i.e. the entry into global DNS, as available to this UA) and receive a DNS response message, the response message containing an IP address associated with the host name or domain name contained in the DNS query message. Delay may be aggravated by the user agent having limited bandwidth access to the internet.